Entire operational system should be focused on multi

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Entire operational system should be focused
on multi- Model EPS Obs, Model development,
Data Assimilation, Products, Interpretations
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Global and Regional Ensemble Prediction Systems,
and THORPEX
Ken Mylne and David Richardson
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(No Transcript)
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Background application of ECMWF EPS

• Met Office makes good use of ECMWF ensemble for
  medium-range
• Medium-range forecasts based on most-probable
  outcome
• Early warnings of severe weather based on EPS
  probabilities
• Increasing emphasis on risk management tools
• Need for short-range probabilities
• Previous research shows benefit of multi-model
  ensembles

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Global EPS

• Global Ensemble provides
• Perturbed LBCs for LAMEPS
• Global coverage for targeting and forecasts
• Contribution to TIGGE
• Now planned to run to 15 days with 20 members
• Operational collaboration with NCEP and MSC

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Met Office Short-Range EPS Plans

• Nested Global and Regional ensembles for
  short-range
• Grid-lengths
• 90km Global
• 20km Regional
• Around 16 members
• Run to T72
• ETKF initial condition perturbations
• Stochastic physics
• Integrated with observation targeting
• Running for demonstration testing from August
  2005

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Medium-range Ensemble Prediction at ECMWF

• Roberto Buizza1, Martin Leutbecher1, Tim Palmer1
  and Glenn Shutts1,2
• Contributions from Jean Bidlot, Graham Holt,
  Martin Miller, Mark Rodwell, Adrian Simmons and
  Nils Wedi to the development of VAREPS are
  acknowledged.
• 1 European Centre for Medium-Range Weather
  Forecasts (www.ecmwf.int)
• 2 Met Office (www.met-office.gov.uk)

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The four key messages of this talk

• The ECMWF Ensemble Prediction System (EPS) has
  been continuously improving. Results indicate a
  2 day/decade gain in predictability for
  probabilistic products.
• Changes implemented on 28 September 2004 will
  further improve the reliability of tropical
  cyclones track prediction.
• Future changes in the singular vectors are
  expected to improve the accuracy of EPS
  forecasts, especially in the earlier forecast
  range.
• The future implementation of the VAriable
  Resolution EPS is expected to improve the EPS
  accuracy in the early/medium-range, and will
  extend the EPS forecast length to 14 days. VAREPS
  will be the first step of the implementation of a
  seamless EPS.

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The EPS performance has been continuously
increasing

• These changes helped to continuously improve the
  EPS accuracy.
• The continuous improvement is shown, e.g., by the
  time evolution of three accuracy measures,
  ROCAfgtc, BSSfgtc and RPPS.

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Over NH, Z500 EPS predictability has increased by
2d/dec

• Results indicate that considering Z500 d5 and
  d7 forecasts over NH
• The EPS control has improved by 1 day/decade
• The EPS ens-mean has improved by 1.5
  day/decade
• The EPS probabilistic products have improved by
  2-3 day/decade

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ECMWF, MSC and NCEP performance for 3 month
(JJA02)

• Recent studies 2,9 have shown that, accordingly
  to many accuracy measures, the ECMWF EPS can be
  considered the most accurate single-model
  ensemble system.
• This is shown, e.g., by the comparison of the EV
  of 10-member ensembles based on the ECMWF, MSC
  (Meteorological Service of Canada) and NCEP
  (National Centers for Environmental Predictions)
  EPSs 9 (Z500 over NH).
• EV, the potential economic value, is the
  reduction of the mean expenses with respect to
  the reduction that can be achieved by using a
  perfect forecast 4,16.

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ECMWF, MSC and NCEP performance for 3 month
(JJA02)

• The ECMWF leading performance 9, estimated to
  be equivalent to a gain of 1 day of
  predictability, has been linked to
• A better analysis
• A better model
• A better estimation of the PDF of forecast
  states.
• This latest point can be seen, e.g., by comparing
  the ensemble spread and the ensemble-mean
  forecast error of 10-member ensembles based on
  the NCEP, MSC and ECMWF EPSs (Z500 over NH).

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The Sep 04 change in the definition of TR-SVs
target areas

• On 28 Sep, one major change was introduced in the
  EPS. In the new system
• Target areas are computed considering TCs
  predictions
• Areas are allowed to extend north of 30ºN
• Up to 6 areas can now be targeted
• Tropical depression (WMO cl?1) detected between
  40S-40N are targeted
• SVs are computed using a new ortho-normalization
  procedure

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Impact of the Sep 04 change in the TR-SVs
target areas
Results based on 44 cases (from 3 Aug to 15 Sep
2004) indicate that the implemented changes in
the computation of the tropical areas has a
positive impact on the reliability diagram of
strike probability.
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VAREPS definition, and planned implementation
schedule

• VAREPS configuration
• D0-7 TL399L40, dt1800s
• D7-14 TL255L40, dt2700s
• Rationale predictability of small scales is
  lost relatively earlier in the forecast range.
  Therefore, while forecasts benefit from a
  resolution increase in the early forecast range,
  they do not suffer so much from a resolution
  reduction in the long range.
• Implementation Q3-Q4 2004

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NRL Ensemble Research Carolyn Reynolds
(reynolds_at_nrlmry.navy.mil)
New (NCAR-NRL) ensemble perturbation system based
on NAVDAS analysis error variance estimates.
Larger amplitudes in the tropics and sub-tropics
than the current operational (bred-mode) scheme.
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NRL Ensemble Research
30N-70N
20S-20N
New method has comparable or better mean skill
than current (above). Rank histograms (right)
shows new method still under dispersive, though
better than current system. (Results for 850-mb
U April 01-10)
Preliminary results Comparable (better)
performance in the mid-latitudes (tropics).
Current and future work will consider model error
and ensemble transform (Bishop and Toth, 1999)
for both global and mesoscale.